To date, the applicant has proposed constitutions of various types of ballpoint pens and filed patent applications thereon.
For example, a ballpoint pen disclosed in Patent Document 1 has an outer tube part capable of being screwed onto a writing tool body. During use, the writing tool body is covered from the outside, and thus the ballpoint pen can have a thickness suitable for being gripped. On the other hand, when not in use, a lead tip or a pen tip is covered from the outside, and thus not only can falling or vibration of the pen be prevented from causing damage to the tip, but the tip can be prevented from causing a puncture wound when the pen is pocketed.
Since a ballpoint pen disclosed in Patent Document 2 has a damper element having a specific structure in a shaft tube, elastic force of a refill spring can be reduced if necessary when a refill and a rotor retreat, and thus comfortable operation of a knock part can be realized.
Thereupon, recently, a slim type ballpoint pen has been required which has a small-diameter shaft tube so as to be realized compactly supported state in a pocket and speedy writing by simple gripping.
However, a specific device in designing for making a slim type ballpoint pen has not been created in the inventions disclosed not only in Patent Documents 1 and 2 but also in other publications.